The Duchess of Sussex's estranged sister, Samantha Markle, has been placed on a police watch list following her repeated attempts to contact the royal.

According to a report by The Times, Markle, 53, who lives in Florida, is understood to have been included on a "fixated persons list" by the police royalty and specialist protection unit, due to the "reputational risk" that she poses to the royal family.

Markle claims she is trying to reconcile with her royal sister, pleading for a truce for the sake of their father, Thomas, who is ill.

In October, Samantha, who has multiple sclerosis and uses a wheelchair, showed up unannounced outside Kensington Palace hoping for a face-to-face meeting with Meghan. But Samantha was turned away by palace guards, however, she was seen giving them a letter before being forced to leave.

She sent Meghan a Christmas card in December, writing that "the time is now" for her to reconcile with their father "in his last years". Samantha wrote, "Holidays are a time for family . . . Dad has been trying to contact you and is very hurt because you are avoiding him".

The Duchess of Sussex will return to royal duties in January, following the Christmas break. (Getty)

According to The Times, Meghan’s personal protection officers are believed to have briefed detectives from Scotland Yard’s Fixated Threat Assessment Centre (FTAC) about the embarrassment that Samantha could cause if she attempts another public rapprochement.

The publication quotes a Scotland Yard source saying, "You can’t protect someone like the Duchess of Sussex without knowing the background of her family. But someone like Samantha presents a risk rather than a threat. She is not committing criminal offences, but she is causing concerns for the royal family."

The source says Samantha's actions could bring "major embarrassment for the royals".

Meghan, 37, is due to give birth to her first child next year, and will resume royal duties in January following the Christmas break.

This morning, Samantha has tweeted a series of denials, saying "that fake news is the most ridiculous malarkey I’ve ever heard".

Samantha Markle has slammed the reports as 'fake news'. (Twitter)

"You will not suppress my right to freedom of speech especially since what I speak is the truth and advocates doing the right thing.

"And you do not call me fixated or say that I harassed public figures when I have no history of that and speaking out for the kind treatment of our father and advocating for doing the right thing does not constitute harassing anyone #FreedomOfSpeech."

She also tweeted a photo of her in a wheelchair with the caption, "Yeah I’m on a fake news watchlist LOL you better watch out or still run your toes over in her wheelchair".

Her father, Thomas, has spoken publicly several times, including Good Morning Britain where he said he'd felt "shunned and ghosted" by his daughter. He then appealed to the Queen for help, saying: "I would think she would want to resolve family problems".

In a statement to The Times Scotland Yard said: "We do not confirm the identity of any person who may or may not be of interest to the police unless that person has been charged".